Message: ...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1833: invalid capture index
Time: Sun Aug 11 14:28:46 2019
Count: 3
Stack: ...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1833: invalid capture index
[C]: in function `find'
...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1833: in function <...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1830>

Locals: (*temporary) = "Steinhauereber stirbt, Ihr bekommt 114 Erfahrung. (+57 Erf. Erholt Bonus)"
(*temporary) = "%1$s stirbt, Ihr bekommt %2$d Erfahrung."

Message: ...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1833: invalid capture index
Time: Sun Aug 11 14:32:45 2019
Count: 1
Stack: ...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1833: invalid capture index
[C]: in function `find'
...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1833: in function <...erface\AddOns\ShestakUI\Libs\LiteStats\LiteStats.lua:1830>

Locals: (*temporary) = "Ihr bekommt 800 Erfahrung."
(*temporary) = "%1$s stirbt, Ihr bekommt %2$d Erfahrung."

I haven't had this issue with the enUS locale. Does this problem occur if you run the game client in English instead of German? Did this occur without any other addons running?

Fixed in eaf5551. Seemed to be specific to German clients with how placeholders for the string localization.